Metal oxide and organo-metal oxide compositions, including gel compositions comprising metal oxide and/or organo-metal oxides, are utilized in a variety of applications including insulation; particulate additives, including flatting agents, thickeners, fillers and reinforcing agents; adsorbents; catalyst supports; membranes; filters; radiation detectors; coatings; and dielectrics. Metal oxide and organo-metal compositions which are utilized in these applications include, but are not limited to, oxides and organo-oxides of silicon, titanium, zirconium, aluminum, iron, magnesium, molybdenum, manganese, boron, copper, zinc, vanadium, tin, nickel, tantalum, niobium, lead, yttrium or mixtures thereof. The term organo-metal oxide refers to a composition comprising a metal oxide and an organic material (i.e. a material comprising CH.sub.x functionality) which may additionally comprise other chemical groups.
Metal oxide and organo-metal oxide compositions are produced in many forms depending on their intended application. The physical forms of metal oxides and organo-metal oxide solids include powders, whiskers, platelets and fibers.
As set forth above, metal oxide and organo-metal oxide compositions also include gels comprising a metal oxide and organo-metal oxide. The term "gel" encompasses wet gels, including hydrogels and alkagels; and gels dried from the wet gels including aerogels and xerogels. The term "aerogel" was coined by S. S. Kistler in U.S. Pat. No. 2,188,007 and is generally utilized to refer to a gel which has been dried under supercritical temperature/pressure conditions. Gels, in particular aerogels, are utilized in a wide variety of applications, including thermal and acoustic insulation, catalyst supports and carriers, filters and molecular sieves, rheology control agents, reinforcing agents, thickeners and electronics, as well as the applications listed above.
Metal oxide and organo-metal oxide compositions may be produced by the liquid phase hydrolysis of metal oxide and organo-metal oxide precursors. In conventional silica production processes a sodium silicate precursor is often utilized. However, it would be advantageous to have process for producing silica which achieves higher purity levels than processes utilizing sodium silicates. It would also be advantageous to have a process which could be utilized to make organo-metal oxides. It would further be advantageous to have a process which allowed for more control over metal oxide and/or organo-metal oxide properties (e.g. particle size, surface area, etc.) than processes utilizing sodium silicates.
Alkoxide precursors are also often utilized in silica production processes and processes for producing other metal oxide and organo-metal oxides. Alkoxide precursors, however, tend to be more expensive than metal chlorides, and may be disadvantageous for economic reasons. A problem which may arise in liquid phase metal oxide and organo-metal oxide production processes utilizing metal chloride or organometallic chloride precursors is that the high rate of the hydrolysis reaction makes it difficult to control the physical properties (size, surface area, etc.) of the metal oxide and organo-metal oxides produced. Thus alkoxide precursors are often employed, despite their generally higher cost, because alkoxide precursors generally allow more control over reaction rates and thereby make it easier to control the physical properties of the metal oxide and organo-metal oxides produced. It would be advantageous, however, to have a metal oxide and organo-metal oxide production process which could utilize metal chloride or organometallic chloride precursors due to their lower cost, but would still allow control over the physical properties of the metal oxide and organo-metal oxide particles produced.
The production of fine silica particles by the a liquid phase reaction process utilizing a silicon tetrachloride precursor and supercritical extraction has been reported. However, it would be advantageous to have a metal oxide and organo-metal oxide production process which could utilize metal chloride or organometallic chloride precursors and did not require the use of supercritical extraction.
Another problem which often arises in conventional processes for producing metal oxide and organo-metal oxide via the liquid phase hydrolysis of metal oxide and organo-metal oxide precursors is the formation of hard metal oxide and organo-metal oxide agglomerates during drying of the the metal oxide and organo-metal oxide. In addition, in conventional drying processes the metal oxide and organo-metal oxides may shrink during drying. The metal oxide and organo-metal oxides formed by such conventional processes may have tap densities higher than suitable for certain applications and may not be free flowing. Therefore, it would be advantageous to have a process for producing metal oxide and organo-metal oxide compositions which minimizes agglomeration and shrinkage and produces metal oxide and organo-metal oxide powders and gels having low tap densities.